Messages in this thread | | | Date | Tue, 8 Aug 2006 16:58:52 +0900 | From | Horms <> | Subject | Re: [RFC] ELF Relocatable x86 and x86_64 bzImages |
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On Tue, Aug 08, 2006 at 01:23:15AM -0600, Eric W. Biederman wrote: > Horms <horms@verge.net.au> writes: > > > On Mon, Aug 07, 2006 at 09:32:23PM -0700, H. Peter Anvin wrote: > >> Horms wrote: > >> > > >> >I also agree that it is non-intitive. But I wonder if a cleaner > >> >fix would be to remove CONFIG_PHYSICAL_START all together. Isn't > >> >it just a work around for the kernel not being relocatable, or > >> >are there uses for it that relocation can't replace? > >> > > >> > >> Yes, booting with the 2^n existing bootloaders. > > > > Ok, I must be confused then. I though CONFIG_PHYSICAL_START was > > introduced in order to allow an alternative address to be provided for > > kdump, and that previously it was hard-coded to some > > architecture-specific value. > > > > What I was really getting as is if it needs to be configurable at > > compile time or not. Obviously there needs to be some sane default > > regardless. > > CONFIG_PHYSICAL_START has had 2 uses. > 1) To allow a kernel to run a completely different address for use > with kexec on panic. > 2) To allow the kernel to be better aligned for better performance.
Thanks for making that clear
> For maintenance reasons I propose we introduce CONFIG_PHYSICAL_ALIGN. > Which will round our load address up to the nearest aligned address > and run the kernel there. That is roughly what I am doing on x86_64 > at this point. > > s/CONFIG_PHYSICAL_START/CONFIG_PHYSICAL_ALIGN/ gives me well defined > behavior and allows the alignment optimization without getting into > weird semantics. > > Before CONFIG_PHYSICAL_START we _always_ ran the arch/i386 kernel > where it was loaded and I assumed we always would. Since people have > realized better aligned kernels can run better this assumption became > false. Going to CONFIG_PHYSICAL_ALIGN allows us to return to the > simple assumption of always running the kernel where it is loaded > modulo a little extra alignment.
That sounds reasonable to me. Though it is a little less flexible, do you think that could be a problem? Perhaps we could have both, though that would probably be quite confusing.
-- Horms H: http://www.vergenet.net/~horms/ W: http://www.valinux.co.jp/en/
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